Construction Of Cobalt-based Catalysts And The Electrolysis Of Water For Hydrogen Evolution Coupled With HMF Oxidation

The anodic oxygen evolution reaction（OER）of electrocatalytic water splitting for hydrogen production has kinetic-sluggish and low value-added of product O₂,and potential safety hazards mixing with H₂ during electrolysis.Utilizing the thermodynamically more favorable 5-hydroxymethylfurfural（HMF）oxidation reaction can considerably decrease the overpotential to replace the anodic OER.Coupling cathodic hydrogen evolution reaction（HER）with anodic HMF oxidation can improve energy utilization efficiency and obtain high value-added chemicals.In this paper,metal heterojunction and two-dimensional bimetallic organic framework cobalt-based catalytic materials was successfully synthesized,with the purpose of promoting efficient anode HMF conversion and cathode hydrogen production.The phase structure,microscopic morphology,element valence state and electrocatalytic performance of the catalyst in alkaline electrolyte were exploded.It was deeply discussed of the relationship between the physical properties of cobalt-based electrocatalysts and catalytic performance,as well as the HER coupled HMF oxidation reaction mechanism.The detailed contents of this paper are as follows:（1）Construction of metal heterojunction Co₉S₈/Ni₃S₂ bifunctional electrocatalyst and their electrocatalytic performance.The highly conductive metal heterojunction Co₉S₈/Ni₃S₂ bifunctional electrocatalyst was synthesized via in-situ sulfidation method.The phase structure,element valence state and microscopic morphology were characterized by XRD,XPS,SEM and TEM,respectively,after what the catalytic performance of HER and HMF in alkaline electrolyte was explored.Co₉S₈/Ni₃S₂demonstrates high activity in the electrolyte（1 M KOH）with 10 m M HMF,reaching the current density of 100 mA cm^-2 at overpotentials of 1.45 V（vs.RHE）,which decreased by200 m V compared with OER.At the anode,the conversion of HMF is about 98%while the FDCA yield is 94%.Furthermore,the catalytic materials have excellent stability,which was proved by six consecutive electrolysis cycles.In the Co₉S₈/Ni₃S₂ two-electrode electrolysis system,the current density reaches 10 mA cm^-2 at a voltage of 1.46 V to generate H₂ and FDCA,which is lower than that of water splitting（1.61 V）.The constructed metal heterojunction is beneficia to charge transfer,and the main active species for improving the catalytic performance are Ni³⁺.（2）Preparation and performance exploration of CoNiMOF electrocatalysts.CoNiMOF nanosheet bifunctional electrocatalysts were synthesized by hydrothermal method and their phase structure,morphological structure,element valence state and electrocatalytic performance was investigated by means of characterization.At the current density of 10 mA cm^-2,a voltage of 1.31 V vs.RHE of the HMF oxidation reaction,which is far less than 1.51 V vs.RHE for OER.The conversion rate of HMF,yield of FDCA and Faraday efficiency of HMF oxidation were 91%,86.6%and 86%,respectively.In the coupling system of HMF oxidation and HER toward CoNiMOF,the voltage of HMF oxidation（1.58 V）is lower than that of water splitting（1.76 V）.The result not only demonstrated that the unique 2D MOFs microstructure of CoNiMOF but also proved the outstanding HMF oxidation performance and good stability of the catalyst.Using metal heterojunction Co₉S₈/Ni₃S₂ electrocatalysts and CoNiMOF electrocatalysts can effectively reduce the anode potential for hydrogen production from water electrolysis,and realize the coupling of biomass electrochemical synthesis of fine chemicals to produce hydrogen.This study is not only overcome the technical bottleneck of efficient water electrolysis to produce hydrogen but also provide a new idea for the technology development of efficient water electrolysis to produce hydrogen coupled with biomass oxidation,which has a positive role in promoting the realization of carbon peaking and carbon neutrality goals and reducing environmental pollution.